1. Field of the Invention
The present invention relates to an epoxy resin composition which exhibits excellent moisture resistance in a cured article, a process for producing an epoxy resin used in the composition, a novel epoxy resin, and a novel phenol resin which is an intermediate of the novel epoxy resin.
Priority is claimed on Japanese Patent Application No. 2002-300212, filed Oct. 15, 2002, the content of which is incorporated herein by reference.
2. Description of Related Art
Epoxy resins are widely used in the fields of electronics and coatings with high levels of functionality because cured articles thereof obtained by curing with various curing agents are excellent in dimensional stability, electrical insulating properties and chemical resistance. In the field of these epoxy resins, attempts of reducing the density of crosslinks of a cured article are made by using a high-molecular weight difunctional epoxy resin for the purpose of imparting flexibility to the cured article or improving dielectric properties dielectric properties in the fields of electrical and electronic components.
In applications such as underfill materials in the field of semiconductor encapsulant and flexible wiring boards in the field of electrical laminates, which have recently been much in demand, there is required an epoxy resin which can produce cured articles which are flexible and excellent in toughness. As an epoxy resin having these required characteristics, for example, there is known an epoxy resin having increased molecular weight obtained by reacting a liquid bisphenol A type epoxy resin with an aliphatic dicarboxylic acid such as dimer acid or sebacic acid as a molecular chain extender (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 8-53533 (pages 2 to 4)). However, the epoxy resin obtained by this technique is likely to be hydrolyzed and is inferior in moisture or water resistance due to an ester bond existing in the molecular structure.
As a technique which improves dielectric properties by reducing the density of crosslinks by way of increasing a molecular weight of an epoxy resin in applications such as semiconductor encapsulant, for example, there is known a technique of introducing alicyclic structure in the chemical structure of an epoxy resin. For example, an epoxy resin which is given by glycidyl etherification of a phenol resin, which is a polyadduct of phenol and dicyclopentadiene, is known as an epoxy resin having improved dielectric properties for semiconductor encapsulant (see, for example, Japanese Unexamined Patent Application, First Publication No. 2001-240654 (claim 1, paragraph number [0009])).
Such an epoxy resin is excellent in moisture resistance and dielectric properties and is a useful resin because it can lower a dielectric dissipation, but it is not sufficient in the effect of lowering the dielectric constant and it is difficult to apply the epoxy resin to a semiconductor of a high frequency type in the gigahertz range, which has recently been much in demand. Therefore, even if the epoxy resin having an alicyclic structure in its chemical structure which is caused by, for example, polyadduct of phenol and dicyclopentadiene, in order to further improve dielectric properties dielectric properties such as low dielectric constant and low dielectric dissipation factor of the epoxy resin, the viscosity increases and drastic deterioration of moisture resistance and water resistance is caused by the reaction between an epoxy group and a phenolic hydroxyl group, thereby deteriorating solder cracking resistance.